This invention relates to fuel cell systems and, in particular, to fuel cell systems wherein a reformer is used to generate fuel process gas for the fuel cell of the system.
In many systems of this type, the reformer used is a steam reformer in which water and a hydrocarbon fuel such as, for example, methanol or ethanol, are directly mixed in the reformer or in a common conduit leading to the reformer. Systems of this type are disclosed in U.S. Pat. Nos. 3,539,395; 3,607,419; 3,982,962; 3,976,507; 4,001,041; 4,120,787; 4,128,700 and 4,200,682. U.S. Pat. No. 3,615,850 also discloses a system of this type wherein the fuel and water are first mixed together in a heat exchanger and, thereafter, conveyed to the reformer.
While the systems of the above patents provide the needed fuel and water to the reformer, they fail to provide it in a manner which promotes optimum system operation and efficiency. In particular, due to the manner of combining the water and fuel, there is a likelihood of inaccuracies occuring in the amount of each constituent combined. This, in turn, can lead to an insufficient amount of fuel gas being generated. It can also lead to fuel being introduced with the fuel process gas into the fuel cell. Both these effects contribute to reduced fuel cell performance.
Furthermore, the manner of mixing the hydrocarbon fuel and water can cause less than total mixing as well as remnant water in the system when the system is shut down. Failure to properly mix the two constituents results in the effects mentioned above with an attendant reduction in performance. Remnant water in the system, on the other hand, can cuase freezing problems, particularly where the fuel cell system is to be used in colder climates.
It is, therefore, an object of the present invention to provide a fuel cell system and method wherein mixing of hydrocarbon fuel and water occurs on board a power plant, in a manner which does not give rise to the above disadvantages.
It is a further object of the present invention to provide a fuel cell system and method wherein hydrocarbon fuel and water are mixed in volumetrically accurate proportions and in a manner which promotes thorough mixing.
It is yet a further object of the present invention to provide a fuel cell system and method wherein hydrocarbon fuel and water are mixed such that the likelihood of the water freezing upon shutdown is greatly reduced.